Motion Integration over Time and Space

Abstract

The effect of temporal and spatial overlap on globally coherent motion was studied. Two lines oriented 60° and 300°, respectively, moved horizontally, creating the perception of either an integrated coherent motion on the horizontal axis, or two distinct component motions orthogonal to each line. The overlap of presentation time was varied: 100% (simultaneous), 50% (partial overlap), and 0% (successive). With respect to the spatial condition, the two lines were presented (1) superimposed in a single aperture, (2) in two adjacent apertures, or (3) in two distant apertures. We found that, when the lines were presented simultaneously, the percentage of perceived coherent motion was consistently high, regardless of spatial condition. However, when temporal overlap was lower, the percentage of perceived coherent motion decreased according to the number of apertures and their distance. In the 0% condition there were fewer than 50% coherent motions reported, even in the single-aperture condition. An effect of the intersection of the two lines was observed in the 50% condition, but not in the 100% condition. These and other findings suggest that timing is the most critical factor, and spatial effects, as expressed by the distance between the lines and by the intersections, play a less important role.